The present invention relates generally to a measurement for an optical performance of an optical system under test and more particularly to a measuring apparatus that measures a wave front aberration of a projection optical system that transfers a pattern of a reticle onto an object, and an exposure apparatus having the same.
A projection exposure apparatus is used to transfer a pattern on a reticle (or a mask) onto an object to be exposed in manufacturing devices, such as semiconductor devices, e.g., an IC and a LSI, image pick-up devices, such as a CCD, display devices, such as a liquid crystal panel, and magnetic heads, in the photolithography process. This exposure apparatus is required to transfer the pattern on the reticle onto the object precisely at a predetermined magnification. For this purpose, it is important to use a projection optical system having good imaging performance and reduced aberration. In particular, due to the recent demands for finer processing to the semiconductor device, a transferred pattern is more sensitive to the aberration of the optical system. Therefore, there is a demand to measure the optical performance, such as a wave front aberration, of the projection optical system with high precision.
A conventional method that actually exposes a reticle pattern onto a wafer, and observes and inspects the resist image using a scanning electron microscope (‘SEM’) or another means has a problem in a long time inspection due to the exposure and development, difficult SEM operations, and bad inspection reproducibility due to errors caused by resist applications and developments. Accordingly, as a solution for these problems, various measuring apparatuses have conventionally been proposed, such as a point diffraction interferometer (“PDI”) that has a pinhole used to form an ideal spherical wave, a shearing interferometer, such as a lateral shearing interferometer (“LSI”), or a Talbo interferometer that utilizes the shearing interferometer, and a line diffraction interferometer (“LDI”) that has a slit used to form an ideal cylindrical wave or an ideal elliptical wave. See, for example, Japanese Patent Applications, Publication Nos. 57-64139, 2000-146705, and 2000-97666.
Nevertheless, the conventional entire system that includes the measuring apparatus and exposure apparatus separately is large and structurally complex, causing the increased cost and the long measuring time. Accordingly, applicant has already proposed an exposure apparatus equipped with an interferometer in Japanese Patent Application, Publication No. 2005-156506.
However, a curved of the interference fringes and a pitch difference increase according to the demands for finer processing to the circuit pattern and higher a numerical aperture (“NA”) of the projection optical system, and a shearing ratio (an amount corresponding to a shift amount between a 0th order light and ±1st order light) particularly changes according to positions. Then, the inventor discovered that the above interferometer cannot maintain the high precision measurement, if the NA of the projection optical system becomes a predetermined value or more.